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			<h1>Java 网络编程</h1>
<p>
网络编程是指编写运行在多个设备（计算机）的程序，这些设备都通过网络连接起来。</p><p>
java.net 包中 J2SE 的 API 包含有类和接口，它们提供低层次的通信细节。你可以直接使用这些类和接口，来专注于解决问题，而不用关注通信细节。</p><p>
java.net 包中提供了两种常见的网络协议的支持：</p>
<ul>
	<li><p><strong>TCP</strong>：TCP（英语：Transmission Control Protocol，传输控制协议） 是一种面向连接的、可靠的、基于字节流的传输层通信协议，TCP 层是位于 IP 层之上，应用层之下的中间层。TCP 保障了两个应用程序之间的可靠通信。通常用于互联网协议，被称 TCP / IP。</p></li>
	<li><p><strong>UDP</strong>：UDP （英语：User Datagram Protocol，用户数据报协议），位于 OSI 模型的传输层。一个无连接的协议。提供了应用程序之间要发送数据的数据报。由于UDP缺乏可靠性且属于无连接协议，所以应用程序通常必须容许一些丢失、错误或重复的数据包。</p></li>
</ul>
<p>本教程主要讲解以下两个主题。</p>
<ul>
	<li><p><strong>Socket 编程</strong>：这是使用最广泛的网络概念，它已被解释地非常详细。</p></li>
	<li><p><strong>URL 处理</strong>：这部分会在另外的篇幅里讲，点击这里更详细地了解在 <a href="../java/java-url-processing.html" title="java url处理" target="_blank" rel="noopener">Java 语言中的 URL 处理</a>。</p></li>
</ul>
<hr>
<h2>
Socket 编程
</h2>
<p>
套接字使用TCP提供了两台计算机之间的通信机制。 客户端程序创建一个套接字，并尝试连接服务器的套接字。</p><p>
当连接建立时，服务器会创建一个 Socket 对象。客户端和服务器现在可以通过对 Socket 对象的写入和读取来进行通信。</p><p>
java.net.Socket 类代表一个套接字，并且 java.net.ServerSocket 类为服务器程序提供了一种来监听客户端，并与他们建立连接的机制。</p><p>
以下步骤在两台计算机之间使用套接字建立TCP连接时会出现：</p>
<ul>
	<li><p>服务器实例化一个 ServerSocket 对象，表示通过服务器上的端口通信。</p></li>
	<li><p>服务器调用 ServerSocket 类的 accept() 方法，该方法将一直等待，直到客户端连接到服务器上给定的端口。</p></li>
	<li><p>服务器正在等待时，一个客户端实例化一个 Socket 对象，指定服务器名称和端口号来请求连接。</p></li>
	<li><p>Socket 类的构造函数试图将客户端连接到指定的服务器和端口号。如果通信被建立，则在客户端创建一个 Socket 对象能够与服务器进行通信。</p></li>
	<li><p>在服务器端，accept() 方法返回服务器上一个新的 socket 引用，该 socket 连接到客户端的 socket。</p></li>
</ul><p>
连接建立后，通过使用 I/O 流在进行通信，每一个socket都有一个输出流和一个输入流，客户端的输出流连接到服务器端的输入流，而客户端的输入流连接到服务器端的输出流。
</p><p>TCP 是一个双向的通信协议，因此数据可以通过两个数据流在同一时间发送.以下是一些类提供的一套完整的有用的方法来实现 socket。
</p>
<hr>
<h2>
ServerSocket 类的方法</h2>
<p>

服务器应用程序通过使用 java.net.ServerSocket 类以获取一个端口,并且侦听客户端请求。</p><p>
ServerSocket 类有四个构造方法：</p>
<table class="reference">
	<tbody>
		<tr>
			<td>
				<strong>序号</strong></td>
			<td style="text-align: center;">
				<strong>方法描述</strong></td>
		</tr>
		<tr>
			<td>
				1</td>
			<td>
				<strong>public ServerSocket(int port) throws IOException</strong><br>
				创建绑定到特定端口的服务器套接字。</td>
		</tr>
		<tr>
			<td>
				2</td>
			<td>
				<strong>public ServerSocket(int port, int backlog) throws IOException</strong><br>
				利用指定的 backlog 创建服务器套接字并将其绑定到指定的本地端口号。</td>
		</tr>
		<tr>
			<td>
				3</td>
			<td>
				<strong>public ServerSocket(int port, int backlog, InetAddress address) throws IOException</strong><br>
				使用指定的端口、侦听 backlog 和要绑定到的本地 IP 地址创建服务器。</td>
		</tr>
		<tr>
			<td>
				4</td>
			<td>
				<strong>public ServerSocket() throws IOException</strong><br>
				创建非绑定服务器套接字。</td>
		</tr>
	</tbody>
</table>
<p>
创建非绑定服务器套接字。 如果 ServerSocket 构造方法没有抛出异常，就意味着你的应用程序已经成功绑定到指定的端口，并且侦听客户端请求。
</p><p>这里有一些 ServerSocket 类的常用方法：</p>
<table class="reference">
	<tbody>
		<tr>
			<td>
				<strong>序号</strong></td>
			<td style="text-align: center;">
				<strong>方法描述</strong></td>
		</tr>
		<tr>
			<td>
				1</td>
			<td>
				<strong>public int getLocalPort()</strong><br>
				&nbsp;&nbsp;返回此套接字在其上侦听的端口。</td>
		</tr>
		<tr>
			<td>
				2</td>
			<td>
				<strong>public Socket accept() throws IOException</strong><br>
				侦听并接受到此套接字的连接。</td>
		</tr>
		<tr>
			<td>
				3</td>
			<td>
				<strong>public void setSoTimeout(int timeout)</strong><br>
				&nbsp;通过指定超时值启用/禁用 SO_TIMEOUT，以毫秒为单位。</td>
		</tr>
		<tr>
			<td>
				4</td>
			<td>
				<strong>public void bind(SocketAddress host, int backlog)</strong><br>
				将&nbsp;ServerSocket&nbsp;绑定到特定地址（IP 地址和端口号）。</td>
		</tr>
	</tbody>
</table>
<hr><h2>
Socket 类的方法</h2>
<p>java.net.Socket 类代表客户端和服务器都用来互相沟通的套接字。客户端要获取一个 Socket 对象通过实例化 ，而 服务器获得一个 Socket 对象则通过 accept() 方法的返回值。
</p><p>Socket 类有五个构造方法.</p>
<table class="reference">
	<tbody>
		<tr>
			<td>
				<strong>序号</strong></td>
			<td style="text-align: center;">
				<strong>方法描述</strong></td>
		</tr>
		<tr>
			<td>
				1</td>
			<td>
				<strong>public Socket(String host, int port) throws UnknownHostException, IOException.</strong><br>
				创建一个流套接字并将其连接到指定主机上的指定端口号。</td>
		</tr>
		<tr>
			<td>
				2</td>
			<td>
				<strong>public Socket(InetAddress host, int port) throws IOException</strong><br>
				创建一个流套接字并将其连接到指定 IP 地址的指定端口号。</td>
		</tr>
		<tr>
			<td>
				3</td>
			<td>
				<strong>public Socket(String host, int port, InetAddress localAddress, int localPort) throws IOException.</strong><br>
				创建一个套接字并将其连接到指定远程主机上的指定远程端口。</td>
		</tr>
		<tr>
			<td>
				4</td>
			<td>
				<strong>public Socket(InetAddress host, int port, InetAddress localAddress, int localPort) throws IOException.</strong><br>
				创建一个套接字并将其连接到指定远程地址上的指定远程端口。</td>
		</tr>
		<tr>
			<td>
				5</td>
			<td>
				<strong>public Socket()</strong><br>
				通过系统默认类型的 SocketImpl 创建未连接套接字</td>
		</tr>
	</tbody>
</table>
<p>当 Socket 构造方法返回，并没有简单的实例化了一个 Socket 对象，它实际上会尝试连接到指定的服务器和端口。</p>
<p>
下面列出了一些感兴趣的方法，注意客户端和服务器端都有一个 Socket 对象，所以无论客户端还是服务端都能够调用这些方法。
</p>
<table class="reference">
	<tbody>
		<tr>
			<td>
				<strong>序号</strong></td>
			<td style="text-align: center;">
				<strong>方法描述</strong></td>
		</tr>
		<tr>
			<td>
				1</td>
			<td>
				<strong>public void connect(SocketAddress host, int timeout) throws IOException</strong><br>
				将此套接字连接到服务器，并指定一个超时值。</td>
		</tr>
		<tr>
			<td>
				2</td>
			<td>
				<strong>public InetAddress getInetAddress()</strong><br>
				&nbsp;返回套接字连接的地址。</td>
		</tr>
		<tr>
			<td>
				3</td>
			<td>
				<strong>public int getPort()</strong><br>
				返回此套接字连接到的远程端口。</td>
		</tr>
		<tr>
			<td>
				4</td>
			<td>
				<strong>public int getLocalPort()</strong><br>
				返回此套接字绑定到的本地端口。</td>
		</tr>
		<tr>
			<td>
				5</td>
			<td>
				<strong>public SocketAddress getRemoteSocketAddress()</strong><br>
				返回此套接字连接的端点的地址，如果未连接则返回&nbsp;null。</td>
		</tr>
		<tr>
			<td>
				6</td>
			<td>
				<strong>public InputStream getInputStream() throws IOException</strong><br>
				返回此套接字的输入流。</td>
		</tr>
		<tr>
			<td>
				7</td>
			<td>
				<strong>public OutputStream getOutputStream() throws IOException</strong><br>
				返回此套接字的输出流。</td>
		</tr>
		<tr>
			<td>
				8</td>
			<td>
				<strong>public void close() throws IOException</strong><br>
				关闭此套接字。</td>
		</tr>
	</tbody>
</table>
<hr>
<h2>
InetAddress 类的方法
</h2>
<p>这个类表示互联网协议(IP)地址。下面列出了 Socket 编程时比较有用的方法：</p>
<table class="reference">
	<tbody>
		<tr>
			<td>
				<strong>序号</strong></td>
			<td style="text-align: center;">
				<strong>方法描述</strong></td>
		</tr>
		<tr>
			<td>
				1</td>
			<td>
				<strong>static InetAddress getByAddress(byte[] addr)</strong><br>
				在给定原始 IP 地址的情况下，返回&nbsp;InetAddress&nbsp;对象。</td>
		</tr>
		<tr>
			<td>
				2</td>
			<td>
				<strong>static InetAddress getByAddress(String host, byte[] addr)</strong><br>
				根据提供的主机名和 IP 地址创建 InetAddress。</td>
		</tr>
		<tr>
			<td>
				3</td>
			<td>
				<strong>static InetAddress getByName(String host)</strong><br>
				在给定主机名的情况下确定主机的 IP 地址。</td>
		</tr>
		<tr>
			<td>
				4</td>
			<td>
				<strong>String getHostAddress()&nbsp;</strong><br>
				返回 IP 地址字符串（以文本表现形式）。</td>
		</tr>
		<tr>
			<td>
				5</td>
			<td>
				<strong>String getHostName()&nbsp;</strong><br>
				&nbsp;获取此 IP 地址的主机名。</td>
		</tr>
		<tr>
			<td>
				6</td>
			<td>
				<strong>static InetAddress getLocalHost()</strong><br>
				返回本地主机。</td>
		</tr>
		<tr>
			<td>
				7</td>
			<td>
				<strong>String toString()</strong><br>
				将此 IP 地址转换为&nbsp;String。</td>
		</tr>
	</tbody>
</table>
<hr>
<h2>
Socket 客户端实例</h2>
<p>如下的 GreetingClient 是一个客户端程序，该程序通过 socket 连接到服务器并发送一个请求，然后等待一个响应。
</p>
<div class="example">
<h2 class="example">GreetingClient.java 文件代码：</h2>
<div class="example_code">
<div class="hl-main"><span class="hl-comment">//</span><span class="hl-comment"> 文件名 GreetingClient.java</span><span class="hl-comment"></span><span class="hl-code">
 
</span><span class="hl-reserved">import</span><span class="hl-code"> </span><span class="hl-identifier">java</span><span class="hl-code">.</span><span class="hl-identifier">net</span><span class="hl-code">.*;
</span><span class="hl-reserved">import</span><span class="hl-code"> </span><span class="hl-identifier">java</span><span class="hl-code">.</span><span class="hl-identifier">io</span><span class="hl-code">.*;
 
</span><span class="hl-reserved">public</span><span class="hl-code"> </span><span class="hl-reserved">class</span><span class="hl-code"> </span><span class="hl-identifier">GreetingClient</span><span class="hl-code">
</span><span class="hl-brackets">{</span><span class="hl-code">
   </span><span class="hl-reserved">public</span><span class="hl-code"> </span><span class="hl-types">static</span><span class="hl-code"> </span><span class="hl-types">void</span><span class="hl-code"> </span><span class="hl-identifier">main</span><span class="hl-brackets">(</span><span class="hl-identifier">String</span><span class="hl-code"> </span><span class="hl-brackets">[</span><span class="hl-brackets">]</span><span class="hl-code"> </span><span class="hl-identifier">args</span><span class="hl-brackets">)</span><span class="hl-code">
   </span><span class="hl-brackets">{</span><span class="hl-code">
      </span><span class="hl-identifier">String</span><span class="hl-code"> </span><span class="hl-identifier">serverName</span><span class="hl-code"> = </span><span class="hl-identifier">args</span><span class="hl-brackets">[</span><span class="hl-number">0</span><span class="hl-brackets">]</span><span class="hl-code">;
      </span><span class="hl-types">int</span><span class="hl-code"> </span><span class="hl-identifier">port</span><span class="hl-code"> = </span><span class="hl-identifier">Integer</span><span class="hl-code">.</span><span class="hl-identifier">parseInt</span><span class="hl-brackets">(</span><span class="hl-identifier">args</span><span class="hl-brackets">[</span><span class="hl-number">1</span><span class="hl-brackets">]</span><span class="hl-brackets">)</span><span class="hl-code">;
      </span><span class="hl-reserved">try</span><span class="hl-code">
      </span><span class="hl-brackets">{</span><span class="hl-code">
         </span><span class="hl-identifier">System</span><span class="hl-code">.</span><span class="hl-identifier">out</span><span class="hl-code">.</span><span class="hl-identifier">println</span><span class="hl-brackets">(</span><span class="hl-quotes">&quot;</span><span class="hl-string">连接到主机：</span><span class="hl-quotes">&quot;</span><span class="hl-code"> + </span><span class="hl-identifier">serverName</span><span class="hl-code"> + </span><span class="hl-quotes">&quot;</span><span class="hl-string"> ，端口号：</span><span class="hl-quotes">&quot;</span><span class="hl-code"> + </span><span class="hl-identifier">port</span><span class="hl-brackets">)</span><span class="hl-code">;
         </span><span class="hl-identifier">Socket</span><span class="hl-code"> </span><span class="hl-identifier">client</span><span class="hl-code"> = </span><span class="hl-reserved">new</span><span class="hl-code"> </span><span class="hl-identifier">Socket</span><span class="hl-brackets">(</span><span class="hl-identifier">serverName</span><span class="hl-code">, </span><span class="hl-identifier">port</span><span class="hl-brackets">)</span><span class="hl-code">;
         </span><span class="hl-identifier">System</span><span class="hl-code">.</span><span class="hl-identifier">out</span><span class="hl-code">.</span><span class="hl-identifier">println</span><span class="hl-brackets">(</span><span class="hl-quotes">&quot;</span><span class="hl-string">远程主机地址：</span><span class="hl-quotes">&quot;</span><span class="hl-code"> + </span><span class="hl-identifier">client</span><span class="hl-code">.</span><span class="hl-identifier">getRemoteSocketAddress</span><span class="hl-brackets">(</span><span class="hl-brackets">)</span><span class="hl-brackets">)</span><span class="hl-code">;
         </span><span class="hl-identifier">OutputStream</span><span class="hl-code"> </span><span class="hl-identifier">outToServer</span><span class="hl-code"> = </span><span class="hl-identifier">client</span><span class="hl-code">.</span><span class="hl-identifier">getOutputStream</span><span class="hl-brackets">(</span><span class="hl-brackets">)</span><span class="hl-code">;
         </span><span class="hl-identifier">DataOutputStream</span><span class="hl-code"> </span><span class="hl-identifier">out</span><span class="hl-code"> = </span><span class="hl-reserved">new</span><span class="hl-code"> </span><span class="hl-identifier">DataOutputStream</span><span class="hl-brackets">(</span><span class="hl-identifier">outToServer</span><span class="hl-brackets">)</span><span class="hl-code">;
 
         </span><span class="hl-identifier">out</span><span class="hl-code">.</span><span class="hl-identifier">writeUTF</span><span class="hl-brackets">(</span><span class="hl-quotes">&quot;</span><span class="hl-string">Hello from </span><span class="hl-quotes">&quot;</span><span class="hl-code"> + </span><span class="hl-identifier">client</span><span class="hl-code">.</span><span class="hl-identifier">getLocalSocketAddress</span><span class="hl-brackets">(</span><span class="hl-brackets">)</span><span class="hl-brackets">)</span><span class="hl-code">;
         </span><span class="hl-identifier">InputStream</span><span class="hl-code"> </span><span class="hl-identifier">inFromServer</span><span class="hl-code"> = </span><span class="hl-identifier">client</span><span class="hl-code">.</span><span class="hl-identifier">getInputStream</span><span class="hl-brackets">(</span><span class="hl-brackets">)</span><span class="hl-code">;
         </span><span class="hl-identifier">DataInputStream</span><span class="hl-code"> </span><span class="hl-identifier">in</span><span class="hl-code"> = </span><span class="hl-reserved">new</span><span class="hl-code"> </span><span class="hl-identifier">DataInputStream</span><span class="hl-brackets">(</span><span class="hl-identifier">inFromServer</span><span class="hl-brackets">)</span><span class="hl-code">;
         </span><span class="hl-identifier">System</span><span class="hl-code">.</span><span class="hl-identifier">out</span><span class="hl-code">.</span><span class="hl-identifier">println</span><span class="hl-brackets">(</span><span class="hl-quotes">&quot;</span><span class="hl-string">服务器响应： </span><span class="hl-quotes">&quot;</span><span class="hl-code"> + </span><span class="hl-identifier">in</span><span class="hl-code">.</span><span class="hl-identifier">readUTF</span><span class="hl-brackets">(</span><span class="hl-brackets">)</span><span class="hl-brackets">)</span><span class="hl-code">;
         </span><span class="hl-identifier">client</span><span class="hl-code">.</span><span class="hl-identifier">close</span><span class="hl-brackets">(</span><span class="hl-brackets">)</span><span class="hl-code">;
      </span><span class="hl-brackets">}</span><span class="hl-reserved">catch</span><span class="hl-brackets">(</span><span class="hl-identifier">IOException</span><span class="hl-code"> </span><span class="hl-identifier">e</span><span class="hl-brackets">)</span><span class="hl-code">
      </span><span class="hl-brackets">{</span><span class="hl-code">
         </span><span class="hl-identifier">e</span><span class="hl-code">.</span><span class="hl-identifier">printStackTrace</span><span class="hl-brackets">(</span><span class="hl-brackets">)</span><span class="hl-code">;
      </span><span class="hl-brackets">}</span><span class="hl-code">
   </span><span class="hl-brackets">}</span><span class="hl-code">
</span><span class="hl-brackets">}</span></div>
</div>
</div>
<hr><h2>
Socket 服务端实例
</h2>
<p>
如下的GreetingServer 程序是一个服务器端应用程序，使用 Socket 来监听一个指定的端口。
</p>
<div class="example">
<h2 class="example">GreetingServer.java 文件代码：</h2>
<div class="example_code">
<div class="hl-main"><span class="hl-comment">//</span><span class="hl-comment"> 文件名 GreetingServer.java</span><span class="hl-comment"></span><span class="hl-code">
 
</span><span class="hl-reserved">import</span><span class="hl-code"> </span><span class="hl-identifier">java</span><span class="hl-code">.</span><span class="hl-identifier">net</span><span class="hl-code">.*;
</span><span class="hl-reserved">import</span><span class="hl-code"> </span><span class="hl-identifier">java</span><span class="hl-code">.</span><span class="hl-identifier">io</span><span class="hl-code">.*;
 
</span><span class="hl-reserved">public</span><span class="hl-code"> </span><span class="hl-reserved">class</span><span class="hl-code"> </span><span class="hl-identifier">GreetingServer</span><span class="hl-code"> </span><span class="hl-reserved">extends</span><span class="hl-code"> </span><span class="hl-identifier">Thread</span><span class="hl-code">
</span><span class="hl-brackets">{</span><span class="hl-code">
   </span><span class="hl-reserved">private</span><span class="hl-code"> </span><span class="hl-identifier">ServerSocket</span><span class="hl-code"> </span><span class="hl-identifier">serverSocket</span><span class="hl-code">;
   
   </span><span class="hl-reserved">public</span><span class="hl-code"> </span><span class="hl-identifier">GreetingServer</span><span class="hl-brackets">(</span><span class="hl-types">int</span><span class="hl-code"> </span><span class="hl-identifier">port</span><span class="hl-brackets">)</span><span class="hl-code"> </span><span class="hl-reserved">throws</span><span class="hl-code"> </span><span class="hl-identifier">IOException</span><span class="hl-code">
   </span><span class="hl-brackets">{</span><span class="hl-code">
      </span><span class="hl-identifier">serverSocket</span><span class="hl-code"> = </span><span class="hl-reserved">new</span><span class="hl-code"> </span><span class="hl-identifier">ServerSocket</span><span class="hl-brackets">(</span><span class="hl-identifier">port</span><span class="hl-brackets">)</span><span class="hl-code">;
      </span><span class="hl-identifier">serverSocket</span><span class="hl-code">.</span><span class="hl-identifier">setSoTimeout</span><span class="hl-brackets">(</span><span class="hl-number">10000</span><span class="hl-brackets">)</span><span class="hl-code">;
   </span><span class="hl-brackets">}</span><span class="hl-code">
 
   </span><span class="hl-reserved">public</span><span class="hl-code"> </span><span class="hl-types">void</span><span class="hl-code"> </span><span class="hl-identifier">run</span><span class="hl-brackets">(</span><span class="hl-brackets">)</span><span class="hl-code">
   </span><span class="hl-brackets">{</span><span class="hl-code">
      </span><span class="hl-reserved">while</span><span class="hl-brackets">(</span><span class="hl-reserved">true</span><span class="hl-brackets">)</span><span class="hl-code">
      </span><span class="hl-brackets">{</span><span class="hl-code">
         </span><span class="hl-reserved">try</span><span class="hl-code">
         </span><span class="hl-brackets">{</span><span class="hl-code">
            </span><span class="hl-identifier">System</span><span class="hl-code">.</span><span class="hl-identifier">out</span><span class="hl-code">.</span><span class="hl-identifier">println</span><span class="hl-brackets">(</span><span class="hl-quotes">&quot;</span><span class="hl-string">等待远程连接，端口号为：</span><span class="hl-quotes">&quot;</span><span class="hl-code"> + </span><span class="hl-identifier">serverSocket</span><span class="hl-code">.</span><span class="hl-identifier">getLocalPort</span><span class="hl-brackets">(</span><span class="hl-brackets">)</span><span class="hl-code"> + </span><span class="hl-quotes">&quot;</span><span class="hl-string">...</span><span class="hl-quotes">&quot;</span><span class="hl-brackets">)</span><span class="hl-code">;
            </span><span class="hl-identifier">Socket</span><span class="hl-code"> </span><span class="hl-identifier">server</span><span class="hl-code"> = </span><span class="hl-identifier">serverSocket</span><span class="hl-code">.</span><span class="hl-identifier">accept</span><span class="hl-brackets">(</span><span class="hl-brackets">)</span><span class="hl-code">;
            </span><span class="hl-identifier">System</span><span class="hl-code">.</span><span class="hl-identifier">out</span><span class="hl-code">.</span><span class="hl-identifier">println</span><span class="hl-brackets">(</span><span class="hl-quotes">&quot;</span><span class="hl-string">远程主机地址：</span><span class="hl-quotes">&quot;</span><span class="hl-code"> + </span><span class="hl-identifier">server</span><span class="hl-code">.</span><span class="hl-identifier">getRemoteSocketAddress</span><span class="hl-brackets">(</span><span class="hl-brackets">)</span><span class="hl-brackets">)</span><span class="hl-code">;
            </span><span class="hl-identifier">DataInputStream</span><span class="hl-code"> </span><span class="hl-identifier">in</span><span class="hl-code"> = </span><span class="hl-reserved">new</span><span class="hl-code"> </span><span class="hl-identifier">DataInputStream</span><span class="hl-brackets">(</span><span class="hl-identifier">server</span><span class="hl-code">.</span><span class="hl-identifier">getInputStream</span><span class="hl-brackets">(</span><span class="hl-brackets">)</span><span class="hl-brackets">)</span><span class="hl-code">;
            </span><span class="hl-identifier">System</span><span class="hl-code">.</span><span class="hl-identifier">out</span><span class="hl-code">.</span><span class="hl-identifier">println</span><span class="hl-brackets">(</span><span class="hl-identifier">in</span><span class="hl-code">.</span><span class="hl-identifier">readUTF</span><span class="hl-brackets">(</span><span class="hl-brackets">)</span><span class="hl-brackets">)</span><span class="hl-code">;
            </span><span class="hl-identifier">DataOutputStream</span><span class="hl-code"> </span><span class="hl-identifier">out</span><span class="hl-code"> = </span><span class="hl-reserved">new</span><span class="hl-code"> </span><span class="hl-identifier">DataOutputStream</span><span class="hl-brackets">(</span><span class="hl-identifier">server</span><span class="hl-code">.</span><span class="hl-identifier">getOutputStream</span><span class="hl-brackets">(</span><span class="hl-brackets">)</span><span class="hl-brackets">)</span><span class="hl-code">;
            </span><span class="hl-identifier">out</span><span class="hl-code">.</span><span class="hl-identifier">writeUTF</span><span class="hl-brackets">(</span><span class="hl-quotes">&quot;</span><span class="hl-string">谢谢连接我：</span><span class="hl-quotes">&quot;</span><span class="hl-code"> + </span><span class="hl-identifier">server</span><span class="hl-code">.</span><span class="hl-identifier">getLocalSocketAddress</span><span class="hl-brackets">(</span><span class="hl-brackets">)</span><span class="hl-code"> + </span><span class="hl-quotes">&quot;</span><span class="hl-special">\n</span><span class="hl-string">Goodbye!</span><span class="hl-quotes">&quot;</span><span class="hl-brackets">)</span><span class="hl-code">;
            </span><span class="hl-identifier">server</span><span class="hl-code">.</span><span class="hl-identifier">close</span><span class="hl-brackets">(</span><span class="hl-brackets">)</span><span class="hl-code">;
         </span><span class="hl-brackets">}</span><span class="hl-reserved">catch</span><span class="hl-brackets">(</span><span class="hl-identifier">SocketTimeoutException</span><span class="hl-code"> </span><span class="hl-identifier">s</span><span class="hl-brackets">)</span><span class="hl-code">
         </span><span class="hl-brackets">{</span><span class="hl-code">
            </span><span class="hl-identifier">System</span><span class="hl-code">.</span><span class="hl-identifier">out</span><span class="hl-code">.</span><span class="hl-identifier">println</span><span class="hl-brackets">(</span><span class="hl-quotes">&quot;</span><span class="hl-string">Socket timed out!</span><span class="hl-quotes">&quot;</span><span class="hl-brackets">)</span><span class="hl-code">;
            </span><span class="hl-reserved">break</span><span class="hl-code">;
         </span><span class="hl-brackets">}</span><span class="hl-reserved">catch</span><span class="hl-brackets">(</span><span class="hl-identifier">IOException</span><span class="hl-code"> </span><span class="hl-identifier">e</span><span class="hl-brackets">)</span><span class="hl-code">
         </span><span class="hl-brackets">{</span><span class="hl-code">
            </span><span class="hl-identifier">e</span><span class="hl-code">.</span><span class="hl-identifier">printStackTrace</span><span class="hl-brackets">(</span><span class="hl-brackets">)</span><span class="hl-code">;
            </span><span class="hl-reserved">break</span><span class="hl-code">;
         </span><span class="hl-brackets">}</span><span class="hl-code">
      </span><span class="hl-brackets">}</span><span class="hl-code">
   </span><span class="hl-brackets">}</span><span class="hl-code">
   </span><span class="hl-reserved">public</span><span class="hl-code"> </span><span class="hl-types">static</span><span class="hl-code"> </span><span class="hl-types">void</span><span class="hl-code"> </span><span class="hl-identifier">main</span><span class="hl-brackets">(</span><span class="hl-identifier">String</span><span class="hl-code"> </span><span class="hl-brackets">[</span><span class="hl-brackets">]</span><span class="hl-code"> </span><span class="hl-identifier">args</span><span class="hl-brackets">)</span><span class="hl-code">
   </span><span class="hl-brackets">{</span><span class="hl-code">
      </span><span class="hl-types">int</span><span class="hl-code"> </span><span class="hl-identifier">port</span><span class="hl-code"> = </span><span class="hl-identifier">Integer</span><span class="hl-code">.</span><span class="hl-identifier">parseInt</span><span class="hl-brackets">(</span><span class="hl-identifier">args</span><span class="hl-brackets">[</span><span class="hl-number">0</span><span class="hl-brackets">]</span><span class="hl-brackets">)</span><span class="hl-code">;
      </span><span class="hl-reserved">try</span><span class="hl-code">
      </span><span class="hl-brackets">{</span><span class="hl-code">
         </span><span class="hl-identifier">Thread</span><span class="hl-code"> </span><span class="hl-identifier">t</span><span class="hl-code"> = </span><span class="hl-reserved">new</span><span class="hl-code"> </span><span class="hl-identifier">GreetingServer</span><span class="hl-brackets">(</span><span class="hl-identifier">port</span><span class="hl-brackets">)</span><span class="hl-code">;
         </span><span class="hl-identifier">t</span><span class="hl-code">.</span><span class="hl-identifier">run</span><span class="hl-brackets">(</span><span class="hl-brackets">)</span><span class="hl-code">;
      </span><span class="hl-brackets">}</span><span class="hl-reserved">catch</span><span class="hl-brackets">(</span><span class="hl-identifier">IOException</span><span class="hl-code"> </span><span class="hl-identifier">e</span><span class="hl-brackets">)</span><span class="hl-code">
      </span><span class="hl-brackets">{</span><span class="hl-code">
         </span><span class="hl-identifier">e</span><span class="hl-code">.</span><span class="hl-identifier">printStackTrace</span><span class="hl-brackets">(</span><span class="hl-brackets">)</span><span class="hl-code">;
      </span><span class="hl-brackets">}</span><span class="hl-code">
   </span><span class="hl-brackets">}</span><span class="hl-code">
</span><span class="hl-brackets">}</span></div>
</div>
</div>
<p>编译以上两个 java 文件代码，并执行以下命令来启动服务，使用端口号为 6066：</p>
<pre>
$ javac GreetingServer.java 
$ java GreetingServer 6066
等待远程连接，端口号为：6066...
</pre><p>
新开一个命令窗口，执行以上命令来开启客户端：</p>
<pre>
$ javac GreetingClient.java 
$ java GreetingClient localhost 6066
连接到主机：localhost ，端口号：6066
远程主机地址：localhost/127.0.0.1:6066
服务器响应： 谢谢连接我：/127.0.0.1:6066
Goodbye!
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	<ol class="commentlist">
		<li class="comment even thread-even depth-1" id="comment-33713"><span class="comt-f">#0</span><div class="comt-avatar wrapper"><i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i><div class="tooltip"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;JeoSaber</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;lov***ming09@163.com</p></div><div id="runoobvote-id-33713" data-commid = "33713" class="upvotejs"><a class="upvote"></a> <span class="count">699</span></div></div><div class="comt-main" id="div-comment-33713"><p>Socket的概念：上面已经解释了，不在复述。</p>

<p><strong>同步和异步：</strong>同步和异步是针对应用程序和内核的交互而言的，同步指的是用户进程触发IO 操作并等待或者轮询的去查看IO 操作是否就绪，而异步是指用户进程触发IO 操作以后便开始做自己的事情，而当IO 操作已经完成的时候会得到IO 完成的通知。</p>

<p>以银行取款为例：</p>

<p><strong>同步</strong> ： 自己亲自出马持银行卡到银行取钱（使用同步 IO 时，Java 自己处理IO 读写）；</p>

<p><strong>异步</strong> ： 委托一小弟拿银行卡到银行取钱，然后给你（使用异步IO 时，Java 将 IO 读写委托给OS 处理，需要将数据缓冲区地址和大小传给OS(银行卡和密码)，OS 需要支持异步IO操作API）；</p>



<p><strong>阻塞和非阻塞：</strong>阻塞和非阻塞是针对于进程在访问数据的时候，根据IO操作的就绪状态来采取的不同方式，说白了是一种读取或者写入操作方法的实现方式，阻塞方式下读取或者写入函数将一直等待，而非阻塞方式下，读取或者写入方法会立即返回一个状态值。</p>

<p>以银行取款为例：</p>

<p><strong>阻塞</strong> ： ATM排队取款，你只能等待（使用阻塞IO时，Java调用会一直阻塞到读写完成才返回）；</p>

<p><strong>非阻塞</strong> ： 柜台取款，取个号，然后坐在椅子上做其它事，等号广播会通知你办理，没到号你就不能去，你可以不断问大堂经理排到了没有，大堂经理如果说还没到你就不能去（使用非阻塞IO时，如果不能读写Java调用会马上返回，当IO事件分发器通知可读写时再继续进行读写，不断循环直到读写完成）</p>

<p><strong>1.BIO 编程</strong></p>

<p>Blocking IO： 同步阻塞的编程方式。</p>

<p>BIO编程方式通常是在JDK1.4版本之前常用的编程方式。编程实现过程为：首先在服务端启动一个ServerSocket来监听网络请求，客户端启动Socket发起网络请求，默认情况下ServerSocket回建立一个线程来处理此请求，如果服务端没有线程可用，客户端则会阻塞等待或遭到拒绝。</p>

<p>且建立好的连接，在通讯过程中，是同步的。在并发处理效率上比较低。大致结构如下：</p>

<p>同步并阻塞，服务器实现模式为一个连接一个线程，即客户端有连接请求时服务器端就需要启动一个线程进行处理，如果这个连接不做任何事情会造成不必要的线程开销，当然可以通过线程池机制改善。</p>

<p>BIO方式适用于连接数目比较小且固定的架构，这种方式对服务器资源要求比较高，并发局限于应用中，JDK1.4以前的唯一选择，但程序直观简单易理解。</p>

<p>使用线程池机制改善后的BIO模型图如下:</p>

<p><strong>2.NIO 编程：Unblocking IO（New IO）： 同步非阻塞的编程方式。</strong></p>

<p>NIO本身是基于事件驱动思想来完成的，其主要想解决的是BIO的大并发问题，NIO基于Reactor，当socket有流可读或可写入socket时，操作系统会相应的通知引用程序进行处理，应用再将流读取到缓冲区或写入操作系统。也就是说，这个时候，已经不是一个连接就要对应一个处理线程了，而是有效的请求，对应一个线程，当连接没有数据时，是没有工作线程来处理的。</p>

<p>NIO的最重要的地方是当一个连接创建后，不需要对应一个线程，这个连接会被注册到多路复用器上面，所以所有的连接只需要一个线程就可以搞定，当这个线程中的多路复用器进行轮询的时候，发现连接上有请求的话，才开启一个线程进行处理，也就是一个请求一个线程模式。</p>

<p>在NIO的处理方式中，当一个请求来的话，开启线程进行处理，可能会等待后端应用的资源(JDBC连接等)，其实这个线程就被阻塞了，当并发上来的话，还是会有BIO一样的问题</p>

<p><strong>3.AIO编程：Asynchronous IO： 异步非阻塞的编程方式。</strong></p>

<p>与NIO不同，当进行读写操作时，只须直接调用API的read或write方法即可。这两种方法均为异步的，对于读操作而言，当有流可读取时，操作系统会将可读的流传入read方法的缓冲区，并通知应用程序；对于写操作而言，当操作系统将write方法传递的流写入完毕时，操作系统主动通知应用程序。即可以理解为，read/write方法都是异步的，完成后会主动调用回调函数。在JDK1.7中，这部分内容被称作NIO.2，主要在java.nio.channels包下增加了下面四个异步通道：AsynchronousSocketChannel、AsynchronousServerSocketChannel、AsynchronousFileChannel、AsynchronousDatagramChannel</p>
<p><strong>bio示例</strong></p>

<p>server示例：</p>

<pre>public class Server {

    public static void main(String[] args) {
        int port = genPort(args);
        
        ServerSocket server = null;
        ExecutorService service = Executors.newFixedThreadPool(50);
        
        try{
            server = new ServerSocket(port);
            System.out.println("server started!");
            while(true){
                Socket socket = server.accept();
                
                service.execute(new Handler(socket));
            }
        }catch(Exception e){
            e.printStackTrace();
        }finally{
            if(server != null){
                try {
                    server.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            server = null;
        }
    }
    
    static class Handler implements Runnable{
        Socket socket = null;
        public Handler(Socket socket){
            this.socket = socket;
        }
        @Override
        public void run() {
            BufferedReader reader = null;
            PrintWriter writer = null;
            try{
                
                reader = new BufferedReader(
                        new InputStreamReader(socket.getInputStream(), "UTF-8"));
                writer = new PrintWriter(
                        new OutputStreamWriter(socket.getOutputStream(), "UTF-8"));
                String readMessage = null;
                while(true){
                    System.out.println("server reading... ");
                    if((readMessage = reader.readLine()) == null){
                        break;
                    }
                    System.out.println(readMessage);
                    writer.println("server recive : " + readMessage);
                    writer.flush();
                }
            }catch(Exception e){
                e.printStackTrace();
            }finally{
                if(socket != null){
                    try {
                        socket.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
                socket = null;
                if(reader != null){
                    try {
                        reader.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
                reader = null;
                if(writer != null){
                    writer.close();
                }
                writer = null;
            }
        }
        
    }
    
    private static int genPort(String[] args){
        if(args.length &gt; 0){
            try{
                return Integer.parseInt(args[0]);
            }catch(NumberFormatException e){
                return 9999;
            }
        }else{
            return 9999;
        }
    }
    
}</pre>
<p>2.client示例：</p>

<pre>public class Client {
    public static void main(String[] args) {
        String host = null;
        int port = 0;
        if(args.length &gt; 2){
            host = args[0];
            port = Integer.parseInt(args[1]);
        }else{
            host = "127.0.0.1";
            port = 9999;
        }
        
        Socket socket = null;
        BufferedReader reader = null;
        PrintWriter writer = null;
        Scanner s = new Scanner(System.in);
        try{
            socket = new Socket(host, port);
            String message = null;
            
            reader = new BufferedReader(
                    new InputStreamReader(socket.getInputStream(), "UTF-8"));
            writer = new PrintWriter(
                    socket.getOutputStream(), true);
            while(true){
                message = s.nextLine();
                if(message.equals("exit")){
                    break;
                }
                writer.println(message);
                writer.flush();
                System.out.println(reader.readLine());
            }
        }catch(Exception e){
            e.printStackTrace();
        }finally{
            if(socket != null){
                try {
                    socket.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            socket = null;
            if(reader != null){
                try {
                    reader.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            reader = null;
            if(writer != null){
                writer.close();
            }
            writer = null;
        }
    }
}</pre>
<p>以上只是简单示例，仅供参考！</p><div class="comt-meta wrapper"><span class="comt-author"><a target="_blank" href="javascript:;">JeoSaber</a><div class="tooltip tooltip1"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;JeoSaber</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;lov***ming09@163.com</p></div></span>5年前 (2018-08-07)</div></div></li><!-- #comment-## -->
<li class="comment odd alt thread-odd thread-alt depth-1" id="comment-34584"><span class="comt-f">#0</span><div class="comt-avatar wrapper"><i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i><div class="tooltip"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;一生默默守护你</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;187***86490@163.com</p></div><div id="runoobvote-id-34584" data-commid = "34584" class="upvotejs"><a class="upvote"></a> <span class="count">169</span></div></div><div class="comt-main" id="div-comment-34584"><p>DatagramSocket(UDP)简单示例</p>

<p>服务端：</p>

<pre>public class Server {
    public static void main(String[] args) {
        try {
            DatagramSocket server = new DatagramSocket(5060);
            DatagramPacket packet = new DatagramPacket(new byte[1024], 1024);
            server.receive(packet);
            System.out.println(packet.getAddress().getHostName() + "(" + packet.getPort() + "):" + new String(packet.getData()));
            packet.setData("Hello Client".getBytes());
            packet.setPort(5070);
            packet.setAddress(InetAddress.getLocalHost());
            server.send(packet);
            server.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}</pre>
<p>客户端:</p>

<pre>public class Client {
    public static void main(String[] args){
        try {
            DatagramSocket client = new DatagramSocket(5070);
            DatagramPacket packet = new DatagramPacket(new byte[1024],1024);
            packet.setPort(5060);
            packet.setAddress(InetAddress.getLocalHost());
            packet.setData("Hello Server".getBytes());
            client.send(packet);
            client.receive(packet);
            System.out.println(packet.getAddress().getHostName() + "(" + packet.getPort() + "):" + new String(packet.getData()));
            client.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}</pre><div class="comt-meta wrapper"><span class="comt-author"><a target="_blank" href="javascript:;">一生默默守护你</a><div class="tooltip tooltip1"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;一生默默守护你</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;187***86490@163.com</p></div></span>5年前 (2018-08-30)</div></div></li><!-- #comment-## -->
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	  upload:false,
	 // upload: {url:'/api/comment_upload_file.php',params: null,fileKey: 'upload_file',connectionCount: 1,leaveConfirm: '文件正在上传，您确定离开?'},
	  defaultImage: 'https://www.runoob.com/images/logo.png',
	  codeLanguages: '',
	  autosave: 'editor-content',
	  toolbar: [  'bold','code','ul','ol','image' ]
	});
	editor.on('selectionchanged', function() {
		$(".code-popover").hide();
	});

	// 提交数据
	$("#share_code").click(function() {
		$(".comment-signarea").hide();
		$("#commentform").show();
		
	});
	$("#user_add_note").click(function() {
		$(".comment-signarea").hide();
		$("#commentform").show();
		$('html, body').animate({
       	    scrollTop: $("#respond").offset().top
    	}, 200);
	});

	// 提交笔记
	var commentform=$('#commentform');
	commentform.prepend('<div id="comment-status" style="display:none;" ></div>');
	var statusdiv=$('#comment-status');
	
	commentform.submit(function(e){
		e.preventDefault();
		var noteContent = editor.getValue();
		// console.log(noteContent);
		noteContent = noteContent.replace(/<pre><code>/g,"<pre>");
		noteContent = noteContent.replace(/<\/code><\/pre>/g,"</pre>");
		
		// 系列化表单数据
		var comment_parent = 0;
		var is_user_logged_in = $("#is_user_logged_in").val();
		var comment_post_ID =  5133;
		var _wp_unfiltered_html_comment = $("#_wp_unfiltered_html_comment").val();
		var comment = noteContent;
		var author = $("#author").val();
		var url = $("#url").val();
		var email = $("#email").val();
		if(isBlank(author) && is_user_logged_in==0) {
			statusdiv.html('<p  class="ajax-error">请输入昵称！</p>').show();
		} else if(isBlank(email)  && is_user_logged_in==0) {
			statusdiv.html('<p  class="ajax-error">请输入邮箱！</p>').show();
		} else {
			// var formdata=commentform.serialize() + "&comment=" + noteContent ;
			// 添加状态信息
			statusdiv.html('<p>Processing...</p>').show();
			// 获取表单提交地址
			var formurl=commentform.attr('action');
			
			// 异步提交
			$.ajax({
					type: 'post',
					url: formurl,
					dataType:'json',
					data: {"comment_parent":comment_parent,"comment_post_ID":comment_post_ID, "_wp_unfiltered_html_comment":_wp_unfiltered_html_comment,"comment":comment,"url":url, "email":email,"author":author},
					error: function(XMLHttpRequest, textStatus, errorThrown){
					statusdiv.html('<p class="ajax-error" >数据不完整或表单提交太快了！</p>').show();
				},
				success: function(data, textStatus){
					if(data.errorno=="0") {
						$("#submit").prop('disabled', true);
						statusdiv.html('<p class="ajax-success" >笔记已提交审核，感谢分享笔记！</p>').show();
						alert('笔记已提交审核，感谢分享笔记！');
					}else{
						statusdiv.html('<p class="ajax-error" >'+data.msg+'</p>').show();
					}
					commentform.find('textarea[name=comment]').val('');
				}
			});
			setTimeout(function(){
		        $("#submit").prop('disabled', false);
		    }, 10*1000);
		}
		return false;

	});
	$(".comt-author").click(function() {
		href = $(this).children("a").attr("href");
		if(href.indexOf("/note/")!=-1) {
			var win = window.open(href, '_blank');
  			win.focus();
		}
	});
	$(".comt-meta span").hover(function(){
		$(this).children(".tooltip").css({ "opacity": 1, "pointer-events": "auto"});
	},function(){
		$(this).children(".tooltip").removeAttr("style");
	});
	/*
	$(".wrapper i").hover(function(){
		$(this).siblings(".tooltip").css({ "opacity": 1, "pointer-events": "auto"});
	},function(){
		$(this).siblings(".tooltip").css({ "opacity": 0, "pointer-events": "auto"});
	});
	*/
	//Upvote.create('runoobvote-id', {callback: vote_callback});
	var ajaxurl = 'https://www.runoob.com/wp-admin/admin-ajax.php';
	var callback = function(data) {
		//console.log($('#runoobvote-id').upvote('upvoted'));
		//console.log($('#runoobvote-id').upvote('downvoted'));
		//console.log(data);
		_vote_action = data.action;
		id_arr = data.id.split('-');
		um_id= id_arr[2];
		//console.log(um_id);
		
		var re = /^[1-9]+/;
		if (re.test(um_id)) { 
			var ajax_data = {
				_vote_action: _vote_action,
				action: "pinglun_zan",
				um_id: um_id,
				um_action: "ding"
			};
			//console.log(ajax_data);
			$.post(ajaxurl,ajax_data,function(status){
				//if(status.vote_num>999) {
				//	_voteHtml = '<span style="display: block; text-align: center;font-size: 20px; color: #6a737c; margin: 8px 0;">'+kFormatter(status.vote_num) +'</span>';
				//	$("#runoobvote-id-" + um_id + " .count").hide().after(_voteHtml);
				//}
				
			});
		}
	};
	if($('#comments').length && $('.upvotejs').length){
		$('.upvotejs').upvote({id: 5133, callback: callback});
	
		$.post(ajaxurl,{"action":"pinglun_zan","postid":5133},function(data){  
			$(data).each(function(key,value) {
				$("#runoobvote-id-" + value.commid + " .upvote").addClass(value.upvotejs_class);
				$("#runoobvote-id-" + value.commid + " .downvote").addClass(value.downvote_class);
				$("#runoobvote-id-" + value.commid + " .count").text(value.upvote_count);
			})
		},'json');
		
	}
	
	
});
function isBlank(str) {
    return (!str || /^\s*$/.test(str));
}
function kFormatter(num) {
	// return num;
    return Math.abs(num) > 999 ? Math.sign(num)*((Math.abs(num)/1000).toFixed(1)) + 'k' : Math.sign(num)*Math.abs(num)
}

</script>

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